In 2015, over 12,000 Veterans had percutaneous coronary interventions (PCI) in one of the 78 Veterans Affairs (VA) cardiac catheterization laboratories throughout the nation. Most of these PCIs used drug eluting stents, which have lower rates of restenosis and need for repeat interventions than earlier bare metal stents. However, drug eluting stents require longer dual antiplatelet therapy (DAPT) with aspirin and a thienopyridine inhibitor to prevent stent thrombosis and myocardial infarction. Current guidelines recommend 12 months DAPT therapy based on studies of 1st-generation drug eluting stents. However, the largest study to assess DAPT duration suggested less myocardial infarction and stent thrombosis with longer treatment up to 3 years after PCI. More recent studies using newer 2nd-generation drug eluting stents reach conflicting conclusions about the duration of DAPT ranging from 6-12 months to as long as 3 years. Currently, the 2nd-generation drug eluting stents have replaced 1st-generation stents. Furthermore, newer more potent antiplatelet agents may offer lower risks of myocardial infarction and stent thrombosis, but have higher risks of bleeding. The question of duration of DAPT is particularly important in Veterans, as they have 2-4 times the risk of myocardial infarction and death after PCI than patients in the largely non-VA research studies of DAPT duration. This MERIT grant proposal study will identify Veterans receiving PCI between 2012-2016 from the VA Cardiovascular Assessment Reporting and Tracking (CART) database which records procedural details of all PCIs in the VA Health System. We will merge this data with VA administrative databases containing information on drug use and duration, and clinical outcomes of death, myocardial infarction, repeat coronary revascularization (PCI or coronary bypass surgery), stroke, and major bleeding from 2-6 years after the index PCI. We will also merge data on these outcomes from non-VA hospitals using the CMS/Medicare database, and cause specific mortality using National Death Index data. The primary aim of the study will assess the risk of death or myocardial infarction from 6 months after PCI to up to 6 years after PCI. We will compare outcomes in Veterans receiving DAPT for 6-12 months versus more than 12 months therapy to assess whether shorter durations are associated with better outcomes with the newer 2nd-generation drug eluting stents. This grant will also compare the newer DAPT agents (ticagrelor and prasugrel) versus clopidogrel, to examine whether these newer agents are associated with less death or myocardial infarction or more major bleeding. In addition the study will develop a simple score to identify Veterans who may benefit from longer DAPT treatment, versus those who could safely use shorter durations of DAPT therapy. Finally, we will use this data to estimate samples sizes for a definitive clinical trial of the DAPT duration in Veterans receiving PCI with 2nd- generation stents.